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Chapter 5Integumentary System

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5.4 Accessory Skin Structures: Hair • Found everywhere on

human body except palms, soles, lips, nipples, parts of external genitalia, and distal segments of fingers and toes

• Shaft protrudes above skin surface

• Root located below surface; base of root is the hair bulb

• Has 3 concentric layers– Medulla: Central axis– Cortex: Forms bulk of hair– Cuticle: Forms hair surface

ArteryVein

Medulla

Cortex

Cuticle

Arrector pili (smooth muscle)

Dermal root sheath

Matrix

Hair papilla

Hair

(a) Adiposetissue

Hair bulb(base ofhair root)

Hairfollicle

Sebaceousgland

Hair root(below skinsurface)

Hair shaft(above skinsurface)

External epithelialroot sheathInternal epithelialroot sheath

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Hair Structure• Hair follicle

– Dermal root sheath: part of dermis that surrounds the epithelial root sheath

– Epithelial root sheath with internal and external parts. • Hair bulb

– Internal matrix is source of hair– Dermis projects into bulb and is

blood supply

ArteryVein

Medulla

Cortex

Cuticle

Arrector pili (smooth muscle)

Dermal root sheath

Matrix

Hair papilla

Hair

Medulla

Cortex

Cuticle

Hair

Dermal root sheath

Melanocyte

Stratum basale

Basement membrane

Hair follicle

(a)

(b) (c)

Hairpapilla

Matrix(growth zone)

Adiposetissue

Hair bulb(base ofhair root)

Hairfollicle

Sebaceousgland

Hair root(below skinsurface)

Hair shaft(above skinsurface)

External epithelialroot sheathInternal epithelialroot sheath

External epithelialroot sheath

Internal epithelialroot sheath

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Hair Structure

• Hair Color. Caused by varying amounts and types of melanin. Melanin can be black-brown and red

• Muscles. Arrector pili. Type of smooth muscle. – Muscle contraction causes hair to “stand on end”– Skin pushed up by movement of hair follicle

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Accessory Skin Structures: Glands

• Sebaceous Glands– Holocrine (death of

secretory cells)– Oily secretion = sebum– Prevents drying and may

inhibit bacteria– Most empty into hair

follicle• Exceptions: lips, meibomian

glands of eyelids, genitalia

Sweat pores

Sebaceous glandHair follicle

Hair bulb

Duct ofapocrinesweat gland

Apocrinesweat gland

Arrector pili(smooth muscle)

Eccrinesweat gland

Duct of eccrinesweat gland

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Accessory Skin Structures: Glands• Sweat (Sudoriferous) Glands

– Two types traditionally called apocrine and merocrine, but apocrine may secrete in a merocrine or holocrine fashion.

• Merocrine or eccrine. Most common. – Simple coiled tubular glands. – Open directly onto surface of skin. Have own pores. – Coiled part in dermis, duct exiting through epidermis. – Produce isotonic fluid (water and NaCl, but also excretory because sweat

includes ammonia, urea, uric acid and lactic acid). As fluid moves through duct, NaCl is moved by active transport back into the body. Final product is hyposmotic (hypertonic). Sweat.

– Numerous in palms and soles. Absent from margin of lips, labia minora, tips of penis, and clitoris.

• Apocrine. Active at puberty. – Compound coiled tubular, usually open into hair follicles superficial to

opening of sebaceous gland. – Secretion: organic compounds that are odorless but, when acted upon by

bacteria, may become odiferous.– Found in axillae, genitalia (external labia, scrotum), around anus.

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Accessory Skin Structures: Glands• Ceruminous glands: modified merocrine sweat

glands, external auditory meatus.– Earwax (cerumen). Composed of a combination of

sebum and secretion from ceruminous.– Function- In combination with hairs, prevent dirt and

insects from entry. Also keep eardrum supple.

• Mammary glands: modified apocrine sweat glands. Covered with reproductive chapter.

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Accessory Skin Structures: Nails

• Anatomy– Nail body: stratum corneum– Eponychium or cuticle is

corneum superficial to nail body, hyponychium is corneum beneath the free edge

– Matrix and nail bed: cells that give rise to the nail

– Nail root: extends • Growth

– Grow continuously unlike hair– Fingernails grow 0.5-1.2

mm/day; faster than toenails

Free edge

Nail body

Nail grooveNail foldLunula

Cuticle

Nail root

Bone

Nail foldNail body

Nail groove

Epidermis

Bone

Cuticle

Nail body

Nail bed

Free edge

Epidermis

Hyponychium

(a)

(b)

(c)

Nail root(under the skin)

Nailmatrix

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5.5 Physiology of the Integumentary System

• Protection– Against abrasion, sloughing off of bacteria as

desquamation occurs.– Against microorganisms and other foreign

substances. Glandular secretions bacteriostatic and skin contains cells of the immune system.

– Melanin against UV radiation.– Hair on head is insulator and protection against

light, and from abrasion. Eyebrows keep sweat out of the eyes; eyelashes protect eyes from foreign objects. Hair in nose and ear against dust, bugs, etc.

– Nails protect ends of digits, self defense.– Acts as barrier to diffusion of water.

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Physiology of the Integumentary System

• Sensation: Pressure, temperature, pain, heat, cold, touch, movement of hairs.

• Temperature Regulation: sweating and radiation.

– Sweat causes evaporative cooling. – Arterioles in dermis change diameter as

temperature changes. More or less blood flows through the dermis.

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Physiology of the Integumentary System• Vitamin D Production

– Begins in skin; aids in Ca2+ absorption. – Vitamin D (calcitriol): hormone. – Functions of Ca2+

• bone formation, growth, repair• clotting• nerve and muscle function.

– People in cold climates and those who cover the body can be deficient, but calcitriol can be absorbed through intestinal wall.

• Sources: dairy, liver, egg yolks, supplements.

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Physiology of the Integumentary System

• Excretion– Removal of waste products from the body.

• Sweat: Water, salt, urea, ammonia, uric acid.

– Insignificant when compared with kidneys.

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5.6 Effects of Aging on the Integumentary System

• Skin more easily damaged because epidermis thins and amount of collagen decreases

• Skin infections more likely• Wrinkling occurs due to decrease in elastic fibers• Skin becomes drier • Decrease in blood supply causes poor ability to

regulate body temperature• Functioning melanocytes decrease or increase;

age spots• Sunlight ages skin more rapidly